Recently, there has been considerable interest within the detergent industry for laundry detergents which are "compact" and therefore, have low dosage volumes. To facilitate production of these so-called low dosage detergents, many attempts have been made to produce high bulk density detergents, for example with a density of 600 g/l or higher. The low dosage detergents are currently in high demand as they conserve resources and can be sold in small packages which are more convenient for consumers, especially in households where there is a premium on storage space.
Generally, there are two primary types of processes by which detergent granules or powders can be prepared. The first type of process involves spray-drying an aqueous detergent slurry in a spray-drying tower to produce highly porous detergent granules. In the second type of process, the various detergent components are dry mixed just prior to agglomeration with a binder, such as a nonionic surfactant. In the former process, there has been difficulty in attaining high levels of surfactant in the resulting detergent composition, a feature which is necessary for low dosage detergents. More particularly, any increase in the density of granules produced by way of conventional spray drying techniques is limited by the relative amount of surfactant required to be passed through the spray drying tower. Consequently, there is a limit or "ceiling" on the amount of surfactant that can be delivered by a detergent product if it only contains spray dried granules. Moreover, spray dried granules which have high surfactant levels and/or are densified by grinding and/or compaction operations do not have favorable flow properties in that they have a tendency to "cake" while stored in the detergent box, especially under highly humid conditions. Such "caking" is very unacceptable to consumers and can lead to difficulties in "scooping" or otherwise removing the detergent from the box in which it is contained. This problem can also result in improper dosing of the laundering solution resulting in decreased cleaning performance.
The art is also replete with disclosures of forming detergent agglomerates which typically are more dense and thus renders them suitable for low dosage detergent compositions. For example, the prior art discloses a process for preparing high density detergent agglomerates by using two mixers in series. In particular, an admix of starting detergent materials is fed into a high speed mixer/densifier after which the materials are fed into a moderate speed mixer/densifier to increase the bulk density further. The resulting detergent agglomerates are suitable for use in low dosage detergents since they are highly dense and contain increased levels of surfactant as compared to the aforementioned spray dried granules. However, low dosage detergent compositions made exclusively of agglomerates generally are not capable of delivering all of the conventional detergent ingredients necessary for a fully formulated, low dosage, modem detergent product.
Accordingly, despite the above-described disclosures in the art, it would be desirable to have a detergent composition which has sufficient levels of surfactant for modern low dosage use and which exhibits improved flow properties. It would also be desirable for such a detergent composition to have increased cleaning performance.